Memory devices are widely used in a variety of digital electronics. One type of memory device is a dynamic random access memory (DRAM) device. DRAM devices can be used to form low cost high density memory arrays. For example, one of the largest applications for DRAM is as the main memory in modern computers. Unfortunately, due to the dynamic nature of its configuration, the information stored in DRAM will eventually degrade unless periodic memory refresh cycles are performed. Thus, though DRAM memory cells may be small in size, they may also consume large amounts of power due to the refresh requirements.
Another type of memory device is a non-volatile memory (NVM) device that has long data retention without the use of refresh cycles. This memory may also be referred to as static memory. In contrast to DRAM, NVM memory devices maybe more expensive but consumes less power. Some examples of non-volatile memory include read-only memory (ROM) and Flash memory.
System designers therefore need to select the appropriate memory type for the systems they are designing. This means accounting for the trade-offs between size, cost, speed, and volatility of the different memory types. In some cases, more resources (e.g., size and cost) are allocated for memory where multiple types of memory are needed to obtain the desired memory characteristics. For example, utilizing DRAM memory for speed and NVM memory for data retention may increase the overall space and size requirements of the system.
It is therefore desirable to have a memory cell that provides the functionality of both DRAM and NVM memories in a single memory cell, thereby reducing the cost and size of memory arrays while providing dual functionality.